1. Field of the Invention
The present invention relates to a focus adjusting device for a binocular and, more particularly, to an improved focus adjusting mechanism which allows one to readily focus a binocular in a manner suitable for a specific kind of an intended object.
2. Description of the Prior Art
When a binocular is used to view an object which is generally stationary, primary importance is usually placed on fine focus adjustment rather than on the quick focus adjustment. For the fine focus adjustment, ocular lenses of a binocular should preferably stroke back and forth over a relatively short distance per unit rotation angle of a focus adjusting ring. It will be adequate, for example, that one or two rotations of the ring cause the ocular lenses to move over the whole predetermined stroke. Hereinafter, the stroke of the ocular lenses per unit rotation angle of the ring will be referred to as the "ocular lens feed rate" for convenience.
On the other hand, where the telescopic object is quick moving such as, for example, sport competition, horse racing, theatrical performances, and others, quick adjustment is more desired than the fine adjustment so that one can sharply focus the binocular to a movement of the object while chasing it. In this case, a relatively large ocular lens feed rate is preferred such as one which allows the whole predetermined range of ocular lens stroke to be covered by about one half the rotation of the ring or less.
The conflicting demands discussed above may at once be met by manufacturing one type of binoculars with different ocular lens feed rates. Manufacturers in the industry concerned have avoided this, however, because the focus adjusting mechanism and thereby the specifications of various parts and assembling steps have to be matched to each of the different ocular lens feed rates. This has allowed users no control over the choice of the ocular lens feed rates in one type of binoculars.